The present disclosure is particularly directed to an airstream treatment apparatus (ATA) for reducing one or more components of the airstream directed through the ATA. In a preferred embodiment, the ATA comprises at least one corona/Non-Thermal Plasma (NTP) generating region where at least one component of the airstream is reduced. The present disclosure is also directed to methods of using the ATA for treating an airstream, particularly the exhaust gas airstream from a combustion engine, and more particularly the exhaust gas airstream from a compression-ignition (diesel) engine.
Internal combustion engines generate a huge amount of toxic pollution and are subject to increasingly stringent emissions standards. Thus for example, carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), non-methane hydrocarbons (NMHCs) and particulate matter (PM) are subject to stringent emissions regulations, since these compounds result in significant human and environmental damage. See, e.g., U.S. Pat. No. 8,157,902, the contents of which is incorporated herein in its entirety by reference.
In light of the strict regulation of the emissions output of internal combustion engines, a large number of pollution control mechanisms have been implemented or explored for reducing these emissions. In this regard, some systems focus on the removal of already-generated emissions (e.g., catalytic converters, Diesel Particulate Matter (DPM) filters), while others instead alter engine function to reduce the actual generation of particular emission components. Thus, for example, Exhaust Gas Recirculation (EGR) systems decrease the temperature of combustion in the engine cylinders by recirculating a proportion of the exhaust stream back into the cylinder, thereby depriving the mixture in the cylinder of oxygen as well as providing a higher heat capacity mixture. Decreased combustion temperature is highly advantageous, in that less NOx is produced at this lower temperature; however, as for all of these systems there are tradeoffs, in this case the generation of greater PM as a result of lower combustion temperature.
One emission control system that has particular promise is a Non-Thermal Plasma (NTP) system, in which corona generated by high-voltage electrical energy is used to generate “cold” plasma, that is, non-equilibrium plasma where the electrons are “hot” while the other species in the plasma are thermally “cold.” Although NTPs have been shown to have numerous beneficial effects on engine emissions, these systems are very sensitive to design parameters, e.g., they work poorly if the electrode distances are too great, or if carbonaceous material (soot) accumulation causes loss of electrical power via arcing. Thus for example, U.S. Pat. No. 8,157,902 describes an NTP system for the treatment of compressive ignition (diesel) exhaust where the most significant aspect of the design is that of a very elaborately designed and constructed “self-cleaning insulator”.
In light of the above, it would be highly advantageous to develop better emission control devices, and in particular corona/NTP-based emission control devices.